This application is the national phase under 35 U.S.C. xc2xa7371 of prior PCT International Application No. PCT/DK98/00069 which has an International filing date of Feb. 20, 1998 which designated the United States of America.
The present invention relates to a method and a plant for the treatment of organic waste materials in liquid form such as liquid manure from livestock production or sewage.
In order to meet increasing world-wide demands for food, intensive livestock production has become more widespread in recent years, and this trend will undoubtedly continue in the future. While providing important benefits in terms of increased yield and a more efficient production process, intensive livestock production has negative environmental consequences due to the large amount of organic waste that is produced. Intensive production of pigs results in particular in a large amount of liquid manure that can represent a serious environmental problem if not treated and handled correctly. However, technologies have not been available in the past to treat this type of liquid organic waste in an environmentally and economically acceptable manner. As a result, the liquid manure from intensive livestock production has in many cases led to serious environmental problems, for example pollution of ground water by excess manure spread onto fields or otherwise allowed to leach into the ground.
Danish utility model No. DK 95 00113 U3 describes a plant for the treatment of liquid manure, in which the manure is converted to compost, fertilisers, water and biogas. The plant comprises 1) a filtration unit for separating fibrous and particulate material having a size of over 1 mm from the liquid and particles less than 1 mm, the fibrous material being e.g. used as compost, 2) a reactor for the production of biogas, 3) an ultrafiltration unit that retains bacteria and suspended organic material and returns such material to the biogas reactor, 4) a desulphurisation unit that removes hydrogen sulphide from the biogas before the biogas is used for the production of heat and power, 5) a reverse osmosis unit, in which the permeate stream from the ultrafilter is separated into a water fraction and a fertiliser concentrate fraction.
A separation plant for liquid manure referred to as BIOREK(copyright) is known from Bioscan A/S (Odense, Denmark). The BIOREK(copyright) plant is based on the plant described in DK 95 00113 U3 and further contains, between the ultrafiltration unit and the reverse osmosis unit, an ammonia stripper for the removal of ammonia and carbon dioxide from the permeate stream from the ultrafilter. The BIOREK(copyright) plant is described e.g. in a brochure, published October 1997, from Bioscan A/S entitled xe2x80x9cBIOREK(copyright) separation plant for liquid manure, Sandager Skovgaardxe2x80x9d.
The present invention represents a further development of the technology known from DK 95 00113 U3 and from the BIOREK(copyright) plant, allowing surprisingly advantageous results to be obtained in the treatment of liquid manure and other liquid organic waste materials.